Subsonic and supersonic towed aerial target



DeC- 14, 1965 R. NORMAN ETAL 3,223,418

SUBSONIC AND SUPEHSONIC TOWED AERIAL TARGET Filed July 27. 1964 f ma@ IW M f w w 1mi/,M E MN hwt MW mf WQ M Y\\ Gym@ l Wr M m. Qkmm/ w wo* mvSN .qw d r Km mr. N l RN lwMQw Q im lnm n u |w E Q m`1 ml www Q WN vu@ Nhlm United States Patent 3,223,418 SUBSONIC AND SUPERSGNKC TWED AERIALTARGET Robert I. Norman, Birmingham, Ala., and Norman F.

Meullen, Charlotte, N.C., assignors to Hayes International Corporation,a corporation of Delaware Filed July 27, 1964, ser. No. 335,331

4 Claims. (Cl. 273-1053) This application is a continuation-in-part ofour copending application Serial No. 119,080, filed lune 23, 1961, TowedAerial Target, now abandoned.

Our invention relates to towed aerial targets and has for its principaland general object the provision of a target capable of steady flightwhile being towed at subsonic, transonic or supersonic speeds. IHeretofore in this art some targets have been towed by attaching a cableto the nose of the body through a swivel. In flight such targets haverotated about their longitudinal axes, and in fact this rotation hasbeen purposely brought about. Such spinning targets have not beencapable of a wide speed range because the spin rate required forstability could not be held within acceptable limits and consequentlysuch targets have tended to roll, pitch and yaw to a large degree at oneend or the other of their speed range. Targets of the general kindinvolved in this application are equipped with various kinds of devicessuch as means to provide infrared appearance, radio receivers and thelike. The efficiency of such devices in prior targets has beenconsiderably decreased and this is due in large measure to the erraticflight characteristics of such prior targets.

For the exercise or" ground-to-air and air-to-air weapons aerial targetshave been a training tool of military services for quite some time.These were intended to simulate the aircraft against which the weaponswere designed to be used. To further the simulation of speed andaltitude some types of these targets were towed by cables from aircrafthaving comparable performance. As this required level of performanceincreased, it became more and more diicnlt to achieve simulation by atow target system because the same problems of high speed flight besetthe target and cable as those which were encountered by the aircraft. Inthis period free-flight targets gained ascendency, being less encumberedby the problems of older systems. However, free-flight targets requiredcostly propulsion, controls, and supporting equipment that all too oftenbecame an irretrievable loss at the end of one flight. This cost finallydictated the return to captive tow targets, but all of the old problemswere still there. The targets had frontal areas and stabilizing surfaceswith airfoil sections that were incompatible with supersonic speeds. Tomake them smaller would inhibit their ability to represent the fullsized aircraft they were meant to simulate, and even a reduction in sizedoes not guarantee that stable flight characteristics good enough forsubsonic speeds would carry over into the supersonic region.

In view of the foregoing, a prime object of our invention is to providea target capable of being towed throughout the range of speed fromsubsonic to supersonic and which, at all speeds, is aerodynamicallystabilized for straight, non-spinning flight within a very narrow rangeof angle of attack, thus to improve the towing characteristics and toenhance the efficiency of the instruments and devices carried by thetarget.

Another object is to provide a target of the character designated inwhich the point of connection of the tow cable, the center of gravity ofthe target and the centers of lift and side force, i.e., the location ofthe resultants of the forces generated by the surface of the target inthe vertical and horizontal planes, all are related to each 3,223,418Patented Dec. 14, 1965 ICC other in such manner as to result in theaforementioned trim throughout a narrow range of angle of attack, at allspeeds.

Another object is to provide a stable, all speed aerial target which maybe towed from a point along its longitudinal center line near its centerof gravity as distinguished from towing the same from the nose, and inwhich the target is aerodynamically balanced for stable flight.

More specifically, we provide a target which is towed from a position onor near the center of gravity of the vehicle as a whole, and in whichtrim for stable flight, for all practical purposes, is accomplished bymeans of fixed horizontal and vertical wings or surfaces, therebyeliminating the necessity of any adjustable trimming devices.

Briefly, we obtain the foregoing objects by providing a target the bodyof which is symmetrical about its longitudinal axis. The cable from thetowing aircraft is attached directly on the longitudinal center line ofthe target, the cable or end fitting passing through the skin of thefuselage or body of the target. The general configuration of the targetis that of a slender body made up of cylindrical and conic sectionshaving small included angles. The fuselage is of high fineness ratio. Weprovide rearwardly of the center of gravity wings or stabilizingsurfaces mutually perpendicular which are highly swept, low aspect ratioand clipped delta in plan form, and have a low thickness ratio airfoil.Specifically, the general configuration of the fuselage is a body ofrevolution with an overall ineness ratio above seven. The center ofgravity is located between fty and sixty percent of the total length ofthe target aft of the nose. The cable preferably is attached at thecenter of gravity, but at no time at a point farther than about one bodydiameter forwardly of the center of gravity or no more than aboutone-fourth body diameter rearwardly of the center of gravity. Thehorizontal stabilizing surfaces are provided with positively camberedsections which create a zero lift nose-down torque which issubstantially equal and opposite to the nose-up torque resulting fromthe relative positions of the center of gravity and the center ofpressure of the target through which the trimmed lift is negative ordownward. A target constructed in accordance with our invention trimsunder all flight conditions above knots indicated air speed with itsprincipal axis maintained within plus or minus live degrees of theflight path. This is because of the very small variation in aerodynamiccharacteristics with Mach number. Cross coupling of longitudinal andlateral types of motion which can produce dynamic instability are thusminimized. Further, all aerodynamic components of the target, namely thebody and wing surfaces, are selected with regard to minimizing theirsensitivity to Mach number elect. This is done by using a high nenessratio for the body and low thickness ratio for the wing surfaces, bothof which have nearly constant aerodynamic characteristics.

A target illustrating features of our invention is shown in theaccompanying drawings forming a part of this application in which:

FIG. 1 is a somewhat diagrammatic plan view;

FIG. 2 is a somewhat diagrammatic side elevational view;

FIG. 3 is a detail sectional View taken generally along line 3 3 of FIG.2;

FIG. 4 is a detail fragmental sectional view taken generally along line4-4 of FIG. l :and showing the location of the tow connection;

FlG. 5 is a sectional View taken on line 5--5 of FIG. 1; and,

FIG. 6 is a force diagram in side elevation.

Referring now to the drawings for a better understanding `of ourinvention, we show our improved target as embodying a main body portionA and a fore body B. It will be noted that the general Configuration ofthe target may be defined as being a long slender body. Specifically,the ratio of the length of the body as a whole, namely the fore body Band main body A to the diameter of the body part A is a fineness greaterthan seven. Actually, in the target shown the neness ratio approachesabout seventeen.

At the forward or leading end of the fore body part B, we provide apropeller driven generator indicated by the numeral 10.

The body portion A is equipped with horizontal stabilizing surfaces orwings 13. Also, the body portion A is provided with vertical stabilizingsurfaces or wings 14. It will be noted that these sets of surfaces are:arranged in cruciform manner. Further, the vertical surfaces are madeup of what is known in the art as a modied diamond airfoil whereas thehorizontal surfaces are moditied :half-diamond sections. Both sets ofsurfaces have thickness to chord ratios less than ve percent. Theseprovisions materially increase the range of air speeds through whichaerodynamic characteristics are constant.

The center of gravity of the target as a Whole is indicated :at 17. Itwill be especially noted that the center of gravity is forward of theleading edges of both the stabilizing surfaces 13 and 14. With respectto the stabilizing surfaces it will be noticed that their leading edgesare highly swept, that they have low aspect ratios, and are clippeddelta in planform. These provisions all tend to reduce variations instability over large ranges of air speed.

The `tow cable T is attached to a swivel indicated at 18. The swivel inturn is attached to a bolt, rivet or the like 19, which lies on thelongitudinal axis or center line of the target indicated at 21. Inconnection with the location of the attaching point 19, We prefer tolocate the center of gravity 17 relative to this point so that 19 isnever any further forward of 17 than one body diameter, and never anyfurther rearward of 17 than one-fourth body diameter. We locate thehorizontal surfaces 13 to assure that the lift center of pressure of theentire target is a minimum of one body diameter aft of the center ofgravity 17. Likewise, the vertical wings or stabilizing surfaces 14 areplaced so that the side force center of pressure of the overallconfiguration is also a minimum of one body diameter aft of the centerof gravity 17 With the foregoing description in mind, and based uponactual experience and actual ight tests of a target constructed inaccordance therewith, we find that our target flies with thelongitudinal principal axis 21 maintained within plus or minus tivedegrees of the flight path under all flight conditions above 150 knotsindicated air speed. With the tow cable :attached at the relative pointindicated, the effects of weight and atmospheric variations will notmaterially alter the determination of trim angles of .attack for airspeeds above 150 knots, indicated, provided the horizontal wing area andits aft location are such as to keep the trim angle of attackrequirement below tive degrees.

As a specific example of a target which has been successfully ilown atMach 1.7, we cite the following:

The body A was formed of a tube 8 inches in diameter and about 83 incheslong; the fore body part B (excluding the forward cylindrical generatorshown in FIGS. 1 and 2) was formed of a frustum of a cone equal indiameter to the body part at its :aft end and tapering down through alength of 36 inches to about 4.5 inches in diameter adjacent the base ofthe wind driven generator. The height of each of the verticalstabilizers from the surface of the body was about 9.9 inches up to theclipped tip, and the chord was :about 27 inches long at the iin-bodyintersection. Thus, both vertical stabilizers provide a combined exposedarea of 296 square inches. The horizontal stabilizing surfaces extendedoutwardly from the body along the line 22 about 14 inches and extended39 inches along the surface-body intersection. Thus, both horizontalstabilizers provide a combined exposed area of 593 square inches. Theplanform of the surfaces 13 is a clipped delta having a leading edgesweep back angle of 70 degrees and an aspect ratio of about 1.4. Thetaper ratio is one-tenth and they are mounted at zero angle of incidencerelative to the longitudinal center line of the body. In section thesurfaces 13 are modified half diamond shapes having planar lowersurfaces. The maximum depth of the horizontal sections 13 at the rootchord was about 1.54 inches characteristic of a 4% thickness ratioconstant for the entire surface and the camber is thus a positive 2% andextends as shown in FIG. 5. The lines 16aL and 16h are the points ofmaximum thickness of the chord, line 162L lying at about 45% of thechord aft of the leading edge 13a and 1Gb lying at about 55% aft of theleading edge. The overall length of the target was about 13() inches.The center of gravity of the target was about 18 inches forwardly of theleading edge 13a of the horizontal surfaces 13. The tow cable attachmentpoint 19 was located substantially coincident with the Center ofgravity. A target made in accordance with this specific example has beenflown at Mach 1.7, has proven to be aerodynarnically stable and entirelysatisfactory in all respects. The camber of the horizontal surfaces 13was such as to develop a nose-down torque within the range of trimmedangle of attack. This torque rotates the target to produce a negativeangle of attack Where the wings generate a downward lift. This creates anose-up torque suicient to balance the target. We find that byconnecting the tow cable to the target through a pivot in the horizontalplane and perpendicular to the center line adjacent the center ofgnavity and on the horizontal center line of the target, all rollingturques acting upon the target are resisted by the tension of the cable,thereby preventing target spin. The tow cable was attached to a swivel18 which in turn was mounted pivotally so as to permit undrestrictedrotation of the swivel in .a vertical plane containing the target centerline from 45 to 100 degrees to the horizontal, while resisting anyrotation in the lateral plane.

In FIG. 6 we show a force diagram which illustrates how our target istrimmed. The negative lift L of the surface 13 is a result of thepitching moment M, which moment is a resultant of the positivelycambered airfoil section. The moment M forces the nose down until thewing adopts a sufficiently negative angle of attack to generate thenegative lift L. This Ilift acting about the center of gravity 17through arm b equals the moment M. Cable tension T equals anddiametrically opposes the resultant of the drag D and the weight andlift forces F of the target. The angle a is a function of therelationship between D and F. Therefore, when constructed as hereindisclosed, our target trims with less drag and a greater angle a thanany such vehicle having uncambered surfaces 13.

In view of the foregoing it will be apparent that we have devised animproved towed aerial target, and one which may be towed from a positionadjacent the center of gravity thereof and which is aerodynamicallytrimmed for ight within a very narrow range of angle of attack. It willbe understood that the fuselage or body of the target may be tubular andthat the target may house any of the desired instrumentalities common tosuch devices. In the target of our improved design and which has beentested, the same has been equipped with various devices such as infraredsources, radar augmentation, radio receivers and the like. Our targetlends itself to launching and recovery from launchers carried by theaircraft.

While we have shown our invention in but one forni, it will be obviousto those skilled in the art that it is not so limited,I but issusceptible of various changesand modications without departing from thespirit thereof, and we desire, therefore, that only such limitationsshall be placed thereupon as are specically set forth in the appendedclaims.

What we claim is:

1. In a target adapted to be towed through the air at the end of a cableby an aerial vehicle at speeds above Mach 1, a tube-like elongated bodysymmetrical about its longitudinal axis and having an overall iinenessratio greater than seven, a connection for attaching the tow cable tothe body intermediate its ends on the longitudinal center line of thebody in the form of a horizontal pivot extending transversely of thelongitudinal center line of the target and limiting the target torotational movement in a plane defined by the line of pull of the cableand the longitudinal center line of the target, vertical and horizontalstabilizing surfaces located to create a center of lift pressure atleast one body diameter rearwardly of the center of gravity of thetarget, said horizontal surfaces being cambered to create a nosedownpitching moment which is substantially constant throughout subsonic andsupersonic speed ranges of the target, said tow cable connection beinglocated substantially on the center of gravity of the target, thereby toprovide a target which flies with its longitudinal axis substantiallywithin plus or minus 5 degrees of any given flight path at all speedsabove 150 knots indicated air speed.

2. The target of claim 1 in which the aspect ratio of the horizontalstabilizing surfaces is on the order of 1.4 and the thickness ratio ofthe airfoil section of said horizontal stabilizing surfaces is on theorder of about 4%.

3. The target of claim 1 in which the vertical and horizontal surfaceshave thickness to chord ratios less than 5%, the vertical surfaces beingof modied diamond airfoil shape.

4. In a target adapted to be towed through the air at the end of a cableby an aerial vehicle, a *long slender tube-like body symmetrical aboutits longitudinal aXis and having a Iineness ratio greater than seven, atow cable connection on the longitudinal center line of the body in theform of a horizontal pivot extending transversely of the longitudinalcenter line of the target and limiting the target to rotational movementin a plane dened by the line of pull of the cable and the longitudinalcenter line of the target, said two cable connection being located atthe center of gravity of the target, and horizontal and verticalstabilizing surfaces located wholly rearwardly of the cable connectionand being of highly swept low aspect ratio, clipped delta in planformand being of low thickness ratio airfoil shape, said horizontal surfacesbeing constructed of modified half-diamond sections cambered to create anose-down torque substantially equal to the nose-up torque resultingfrom the relative locations of the center of pressure of the target andthe center of gravity of the target.

References Cited by the Examiner UNITED STATES PATENTS 2,551,596 5/1951Haglund.

2,667,351 1/1954 McKinney et al. 273-1053 2,779,553 1/ 1957 Troxell244-3 2,821,396 1/1958 Seeley 273-105.3 2,879,999 3/ 1959 Marshall273-1053 2,930,619 3/1960 Greenwood 273-1053 3,030,111 4/ 1962Hendershott 273-105 .3 3,135,511 6/1964 Norman et al. 273-1053 DELBERTB. LOWE, Primary Examiner.

1. IN A TARGET ADAPTED TO BE TOWED THROUGH THE AIR AT THE END OF A CABLEBY AN AERIAL VEHICLE AT SPEEDS ABOVE MACH 1, A TUBE-LIKE ELONGATED BODYSYMMETRICAL ABOUT ITS LONGITUDINAL AXIS AND HAVING AN OVERALL FINENESSRATIO GREATER THAN SEVEN, A CONNECTION FOR ATTACHING THE TOW CABLE TOTHE BODY INTERMEDIATE ITS ENDS ON THE LONGITUDINAL CENTER LINE OF THEBODY IN THE FORM OF A HORIZONTAL PIVOT EXTENDING TRANSVERSELY OF THELONGITUDINAL CENTER LINE OF THE TARGET AND LIMITING THE TARGET TOROTATIONAL MOVEMENT IN A PLANE DEFINED BY THE LINE OF PULL OF THE CABLEAND THE LONGITUDINAL CENTER LINE OF THE TARGET, VERTICAL AND HORIZONTALSTABILIZING SURFACES LOCATED TO CREATE A CENTER OF LIFT PRESSURE ATLEAST ONE BODY DIAMETER REARWARDLY OF THE CENTER OF GRAVITY OF THETARGET SAID HORIZONTAL SURFACES BEING CAMBERED TO CREATE A NOSEDOWNPITCHING MOMENT WHICH IS SUBSTANTIALLY CONSTANT THROUGHOUT SUBSONIC ANDSUPERSONIC SPEED RANGES OF THE TARGET, SAID TOW CABLE CONNECTION BEINGLOCATED SUBSTANTIALLY ON THE CENTER OF GRAVITY OF THE TARGET, THEREBY TOPROVIDE A TARGET WHICH FLIES WITH ITS LONGITUDINAL AXIS SUBSTANTIALLYWITHIN PLUS OR MINUS 5 DEGREES OF ANY GIVEN FLIGHT PATH AT ALL SPEEDSABOVE 150 KNOTS INDICATED AIR SPEED.